1. Field of the Invention
The invention is directed to a clutch system with a clutch device for arrangement in a drivetrain of a motor vehicle for transmitting torque between a drive unit and a transmission having multiple speeds, the clutch device having at least one multiple-plate clutch arrangement which is associated with a transmission input shaft and which has an inner plate carrier, an outer plate carrier and a plate stack which is arranged between the inner plate carrier and the outer plate carrier. The multiple-plate clutch arrangement is provided for operating by the action of an operating fluid, and for this purpose the clutch system has an operating fluid supply by means of which at least one flow of operating fluid can be supplied to the plate stack from the radial inside of the inner plate carrier toward the radial outside or from the radial outside of the outer plate carrier toward the radial inside.
2. Description of the Related Art
A clutch system of this type is known, for example, from U.S. Pat. No. 6,464,059 and has a dual clutch device, also known as a double clutch, with a first multiple-plate clutch arrangement associated with a first transmission input shaft and a second multiple-plate clutch arrangement associated with a second transmission input shaft. The two multiple-plate clutch arrangements are arranged with their plate stacks and inner and outer plate carriers in the same axial area in such a way that a radial outer plate stack of one clutch arrangement encloses a radial inner plate stack of the other clutch arrangement on the radial outer side.
Operating fluid such as coolant oil must be supplied to the clutch arrangements particularly for slip operation in order to prevent overheating of the plates and possibly burning of the friction facings. In known plate stack constructions, the operating fluid is supplied proceeding from the radial inner side by means of a suitably constructed operating fluid supply which has at least one operating fluid pump (oil pump).
It is necessary to take stock of the energy required for providing the flow of operating fluid. For this reason, it is recommended that the flow of operating fluid be provided only when actually required by slip operation or the like. For this purpose, the present applicant has suggested constructions of the operating fluid supply in various patent applications. With regard to the supply of the flow of operating fluid and a hydraulic pressure medium used for actuation of the clutch arrangements (particularly a hydraulic oil which is also used as coolant oil), the suggested constructions especially favor the use of electrically driven pumps which make it possible to provide the flow of operating fluid and hydraulic pressure medium as needed in a simple manner. Heretofore, it has always been taken for granted that the flow of operating fluid must be minimized for purposes of energy efficiency with respect to the heat to be guided off from the clutch arrangements and that the flow of operating fluid must be initiated only in clutch states requiring the elimination of heat.
The synchronizing work to be performed when engaging gears is particularly important in dual clutches. The synchronizing work to be performed, which is comparatively extensive in such dual clutches under certain conditions, requires synchronizing devices which can sustain a comparatively high load and which are therefore expensive, insofar as an active synchronization by means of the clutch arrangements themselves is impossible. There is a need to relieve the synchronizing devices as far as possible so that the synchronizing work to be carried out is not performed by the synchronizing devices exclusively.
U.S. Pat. No. 5,890,392, for example, suggests providing friction wheels in a dual clutch transmission for active synchronization of the transmission shaft to be shifted. This represents considerable structural expenditure and is consequently cost-intensive.
According to the invention, the operating fluid supply is constructed in such a way that the flow of operating fluid, in particular the cooling fluid, can be switched on and off. A control unit is associated with the operating fluid supply to switch the flow of operating fluid on or off by controlling the operating fluid supply in a corresponding manner in the course of a shifting process in which the transmission is shifted up from a lower gear to a higher gear or down from a higher gear to a lower gear in order to deliberately exert inertial forces on at least one of the plate carriers by means of the flow of operating fluid and, accordingly, in order to act on this plate carrier in an accelerating or decelerating manner or in order to deliberately prevent inertial forces of this type being exerted on at least one of the plate carriers by the flow of operating fluid.
The inventive suggestion is based upon the consideration and the insight that during interaction between the flow of operating fluid and the plate carriers, the latter are acted upon by inertial forces which can reinforce the synchronization with respect to the gear to be engaged (and which to this extent can relieve the synchronizing devices of the transmission) or which can oppose the synchronization (and to this extent load the synchronizing devices of the transmission). Therefore, it is suggested that the flow of operating fluid be switched on and off deliberately in such a way that the synchronizing devices are relieved or are not additionally loaded.
The flow of operating fluid can be supplied to the plate stack from the radial inner side, as disclosed in U.S. Pat. No. 6,464,059. However, it is also possible to supply the flow of operating fluid to the plate stack from the radial outer side (see e.g. U.S. Pat. No. 6,202,814).
According to one embodiment of the invention, the control unit is preferably constructed for deliberately switching on the flow of operating fluid in the course of shifting the transmission up from a lower gear to a higher gear in order to exert inertial forces acting on at least one of the plate carriers for braking the latter for purposes of approximating a synchronizing speed associated with the higher gear.
According to another embodiment of the invention, the control unit is preferably constructed for deliberately switching off the flow of operating fluid in the course of shifting the transmission down from a higher gear to a lower gear in order to prevent inertial forces acting on at least one of the plate carriers for braking the latter for purposes of approximating a synchronizing speed associated with the lower gear.
As was already mentioned, the clutch device can be constructed as a dual clutch device or multiple clutch device and can have a first multiple-plate clutch arrangement associated with a first transmission input shaft and a second multiple-plate clutch arrangement associated with a second transmission input shaft. In contrast to the construction according to U.S. Pat. No. 6,464,059, the clutch arrangements can be arranged axially next to one another and the operating fluid supply has a first supply part associated with the first clutch arrangement and a second supply part which is associated with the second clutch arrangement. The first and second supply parts are controllable by the control unit independent from one another for deliberately switching on and switching off at least a first flow of operating medium allocated to the first clutch arrangement or at least a second flow of operating medium allocated to the second clutch arrangement. In this case, the two clutch arrangements can be regarded as completely independent from one another as regards the synchronizing work and the relief of the synchronizing units or prevention of additional loading of the synchronizing units by inertial forces exerted by the operating fluid.
On the other hand, when the clutch arrangements overlap axially, wherein a radial outer plate stack of one clutch arrangement encloses a radial inner plate stack of the other clutch arrangement on the radial outer side, and when the at least one flow of operating fluid passes the radial inner and radial outer plate stack, it can be taken into account at least when considered in more detail that the flow of operating fluid passes the two plate stacks one after the other. In so doing, the flow first interacts with the plate carriers of one clutch arrangement and then interacts with the plate carriers of the other clutch arrangement, depending on the construction of the plate carriers. In certain operating situations, the plate carriers of one clutch arrangement cause the flow of operating fluid to be accelerated in circumferential direction, and the interaction with the plate carriers of the other clutch arrangement depends upon this acceleration in circumferential direction.
However, as concerns the clutch arrangement whose plate carriers first interact with the flow of operating fluid, the situation respecting the relief of the synchronizing units and the prevention of additional loading of the synchronizing units is the same as in an axial side-by-side arrangement of the clutch arrangements.
Assuming that the flow of operating fluid can be supplied to the radial inner plate stack from the radial inner side, the control unit can be constructed for deliberately switching on the flow of operating fluid in the course of shifting up the transmission from a lower gear associated with the clutch arrangement with the radial outer plate stack to a higher gear associated with the clutch arrangement with the radial inner plate stack in order to exert inertial forces acting on at least one plate carrier of the clutch arrangement with the radial inner plate stack for braking the latter for purposes of approximating a synchronizing speed associated with the higher gear. It is further suggested that this control unit is constructed for deliberately switching off the flow of operating fluid in the course of shifting down the transmission from a higher gear associated with the clutch arrangement with the radial outer plate stack to a lower gear associated with the clutch arrangement with the radial inner plate stack in order to prevent inertial forces acting on at least one plate carrier of the clutch arrangement with the radial inner plate stack for braking the latter for purposes of approximating a synchronizing speed associated with the lower gear.
Further, to take into account the interaction of the flow of operating fluid with the radial outer plate stack and associated plate carriers also, the control unit can advantageously be constructed for deliberately switching on or switching off the flow of operating fluid in the course of shifting up the transmission from a lower gear associated with the clutch arrangement with the radial inner plate stack to a higher gear associated with the clutch arrangement with the radial outer plate stack in order to exert inertial forces acting on at least one plate carrier of the clutch arrangement with the radial outer plate stack so as to brake the latter or to prevent inertial forces acting so as to accelerate the latter for the purpose of approximating a synchronizing speed associated with the higher gear. Further, the control unit can advantageously be constructed for deliberately switching off or switching on the flow of operating fluid in the course of shifting down the transmission from a higher gear associated with the clutch arrangement with the radial inner plate stack to a lower gear associated with the clutch arrangement with the radial outer plate stack in order to prevent inertial forces acting on at least one plate carrier of the clutch arrangement with the radial outer plate stack so as to brake the latter or to exert inertial forces acting so as to accelerate the latter for the purpose of approximating a synchronizing speed associated with the lower gear.
The synchronizing work to be carried out generally depends on the speed-reducing or speed-increasing jump between gears. In this connection, it is suggested that the control unit is constructed so as to adjust the intensity of the at least one flow of operating fluid as a function of a speed-increasing or speed-reducing jump between gears.
It is particularly preferable that at least one of the plate carriers has application formations with application surfaces which extend in radial direction and interact with the flow of operating fluid. By constructing the plate carrier or plate carriers in this way, the inertial forces that can be exerted on the plate carrier or plate carriers by means of the at least one flow of operating fluid can be increased or maximized. In particular, the application formations can also be those not required, per se, for the functioning of the multiple-plate clutch arrangement. For example, the application formations can comprise blades which project radially inward from an inner plate carrier and/or blades which project radially outward from an outer plate carrier. However, constructions which are already provided in standard plate carriers and serve to drive the plates in rotation, for example, and which have surfaces or surface portions extending in radial direction must also be considered as application formations within a broader sense.
The invention is further directed to a motor vehicle drivetrain with a drive unit, a transmission and a clutch system according to the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.